This invention relates to a force detector and an acceleration detector to which the force detector is applied, and more particularly to a detector suitable for detection of multidimensional force or acceleration components. Further, this invention provides a method suitable for mass producing such detectors.
In the automobile industry or the machinery industry, there has been increased demand for detectors capable of precisely detecting a physical quantity such as force, acceleration or magnetism. Particularly, it is required to realize small detectors capable of detecting physical quantities every respective two-dimensional or three-dimensional components.
To meet such a demand, there has been proposed a force detector in which gauge resistors are formed on a semiconductor substrate such as silicon, etc. to transform a mechanical distortion produced in the substrate on the basis of a force applied from the external to an electric signal by making use of the piezo resistive effect. When a weight body is attached to the detecting unit of the force detector, an acceleration detector for detecting, as a force, an acceleration applied to the weight body can be realized. Further, when a magnetic body is attached to the detecting unit of the force detector, a magnetic detector for detecting, as a force, a magnetism exerted on the magnetic body can be realized.
For example, in U.S. Pat. Nos. 4,905,523, 4,967,605, 4,969,366, U.S. patent application Ser. Nos. 07/362,399, 07/470,102, and 07/559,381, force detectors using gauge resistor, acceleration detectors, and magnetic detectors are disclosed. Further, in U.S. patent application Ser. No. 07/526,837, a manufacturing method suitable for these detectors is disclosed.
Since there generally exists temperature dependency in the gauge resistance or the piezo resistive coefficient, in the case of the above described detectors, if there occurs any change in the temperature of the environment where those detectors are used, a detected value would include an error. Accordingly, it is required for carrying out a precise measurement to conduct temperature compensation. Particularly, in the case where such detectors are used in the field of automotive vehicle, etc., temperature compensation is required over the considerably broad operating temperature range of xe2x88x9240 to +12xc2x0 C.
In addition, in order to manufacture the above described detectors, a high level process for processing the semiconductor substrate is required, and a high cost apparatus such as an ion implanter is also required. For this reason, there is the problem that the manufacturing cost becomes high.
A first object of this invention is to provide a novel detector which can detect a physical quantity such as force, acceleration or magnetism, etc. without carrying out temperature compensation, and can be supplied at a low cost.
A second object of this invention is to provide a manufacturing method suitable for mass production of such a novel detector.
1. Feature Relating to the Detector
To attain the above described first object, the detector according to this invention is featured as follows:
(1) The first feature resides in a force detector comprising:
a flexible substrate including a fixed portion fixed to a detector casing, a working portion to which a force from the external is transmitted, and a flexible portion having flexibility formed between the fixed portion and the working portion,
a fixed substrate fixed on the detector casing so as to face the flexible substrate,
a working body adapted to receive a force from the external to transmit this force to the working portion of the flexible substrate,
a displacement electrode formed on the surface facing to the fixed substrate of the flexible substrate, and
a fixed electrode formed on the surface facing to the flexible substrate of the fixed substrate,
wherein any one of the displacement electrode and the fixed electrode, or both the electrodes are constituted by a plurality of electrically independent localized electrodes to form a plurality of capacitance elements by electrodes opposite to each other to detect a force exerted on the working body every multidimensional respective components on the basis of changes in the electrostatic capacitance values of the respective capacitance elements.
In the force detector having the above mentioned first feature, when a force from the external is applied to the working body, the flexible substrate bends, so a distance between the displacement electrode and the fixed electrode varies. Accordingly, an electrostatic capacitance between both electrodes varies. Because the change of the electrostatic capacitance is dependent upon a force applied from the external, detection of force can be made by detecting the change of the electrostatic capacitance. In addition, at least one of the displacement electrode and the fixed electrode is constituted by a plurality of localized electrodes. A change of an electrostatic capacitance of a capacitance element formed by a localized electrode is dependent upon a direction of a force exerted and a position of the local electrode. Accordingly, changes in electrostatic capacitance values of a plurality of capacitance elements formed by a plurality of localized electrodes-include information relating to a direction of the force exerted. Thus, the force exerted can be detected every multidimensional respective components.
(2) In the force detector having the above described first feature, the second feature resides in a force detector,
wherein any one of the displacement electrode and the fixed electrode, or both the electrodes are constituted by four groups of localized electrodes arranged in positive and negative directions of a first axis and a second axis perpendicular to each other on the surface where the localized electrodes are formed (hereinafter referred to as the electrode formation surface), thus to form four groups of capacitance elements by using the four groups of localized electrodes, respectively,
a force component in the first axis direction being detected by a difference between electrostatic capacitance values of capacitance elements belonging to the two groups of capacitance elements on the first axis of the four groups of capacitance elements,
a force component in the second axis direction being detected by a difference between electrostatic capacitance values of capacitance elements belonging to the two groups of capacitance elements on the second axis of the four groups of capacitance elements.
In the force detector having the above described second feature, four groups of localized electrodes are formed. When the electrode formation surface is defined as an XY plane, respective groups are formed on the both positive and negative sides of the X-axis and on the positive and negative sides of the Y-axis, respectively. When a force in the X-axis direction is exerted on the working body, since the electrostatic capacitance values with respect to the both groups positioned on the positive and negative sides of the X-axis complementarily changes, it is possible to detect a force in the X-axis direction by the difference between electrostatic capacitance values with respect to the both groups. Similarly, by the difference between electrostatic capacitance values with respect to the both groups positioned on the positive and negative sides of the Y-axis, it is possible to detect a force in the Y-axis direction.
(3) In the force detector having the above described first feature, the third feature resides in a force detector,
wherein anyone of the displacement electrode and the fixed electrode or both the electrodes are constituted by four groups of localized electrodes arranged in positive and negative directions with respect to a first axis and a second axis perpendicular to each other on the electrode formation surface to form four groups of capacitance elements by using four groups of localized electrodes, respectively,
a force component in the first axis direction being detected by a difference between electrostatic capacitance values of capacitance elements belonging to two groups of capacitance elements on the first axis of the four groups of capacitance elements,
a force component in the second axis direction being detected by a difference between electrostatic capacitance values of capacitance elements belonging to two groups of capacitance elements on the second axis of the four groups of capacitance elements,
a force component in the third axis direction perpendicular to the first axis and the second axis being detected by a sum of electrostatic capacitance values of capacitance elements belonging to four groups of capacitance elements.
In the force detector having the third feature, four groups of localized electrodes are formed. When the electrode formation surface is defined as an XY-plane, respective groups are formed on both the positive and negative sides of the X-axis and on both the positive and negative sides of the Y-axis. When a force in the X-axis direction is exerted on the working body, since the electrostatic capacitance values with respect to both the groups positioned on the positive and negative sides of the X-axis complementarily vary, it is possible to detect a force in the X-axis direction by the differences between electrostatic capacitance values with respect to the both groups. Similarly, it is possible to detect a force in the Y-axis direction by the differences between electrostatic capacitance values with respect to both the groups positioned on the positive and negative sides of the Y-axis. In addition, when a force in the Z-axis direction is exerted on the working body, since the electrostatic capacitance values with respect to the four groups vary in the same direction, it is possible to detect a force in the Z-axis direction by the sum thereof.
(4) In the force detector having the above described first feature, the fourth feature resides in a force detector,
wherein any one of the displacement electrode and the fixed electrode, or both the electrodes are constituted by four groups of localized electrodes respectively arranged in positive and negative directions with respect to a first axis and a second axis perpendicular to each other on the electrode formation surface, and a fifth group of localized electrodes arranged at the intersecting point of the first axis and the second axis to form five groups of capacitance elements by using five groups of localized electrodes, respectively,
a force component in the first axis direction being detected by a difference between electrostatic capacitance values of capacitance elements belonging to two groups of capacitance elements on the first axis of the five groups of capacitance elements,
a force component in the second axis direction being detected by a difference between electrostatic capacitance values of capacitance elements belonging to two groups of capacitance elements on the second axis of the five groups of capacitance elements,
a force component in a third axis perpendicular to the first axis and the second axis being detected by electrostatic capacitance values of capacitance elements using the fifth group of localized electrodes of the five groups of capacitance elements.
In the force detector having the fourth feature, since an exclusive capacitance element for detecting a force component in the third axis direction is formed, more accurate detected values can be provided.
(5) In the force detector having the above described first feature, the fifth feature resides in that the displacement electrode is formed at the working portion.
In the force detector having the fifth feature, since the displacement electrode is efficiently subjected to displacement, the sensitivity can be improved.
(6) In the force detector having the above described first feature, the sixth feature resides in a force detector,
wherein there is further provided an auxiliary substrate so that the fixed substrate, the flexible substrate and the auxiliary substrate are oppositely arranged in order recited, respectively,
wherein a first auxiliary electrode is formed on the surface facing to the auxiliary substrate of the flexible substrate,
wherein a second auxiliary electrode is formed on the surface facing to the flexible substrate of the auxiliary substrate, and
wherein a predetermined voltage is applied across the first auxiliary electrode and the second auxiliary electrode, or across the displacement electrode and the fixed electrode to allow the flexible substrate to produce displacement by a coulomb force exerted therebetween, thus permitting the force detector to be placed in the state equivalent to the state where a force is exerted thereon from the external.
In the force detector having the sixth feature, when a predetermined voltage is applied across respective electrodes, the flexible substrate is permitted to produce displacement by coulomb force exerted therebetween. Namely, the force detector can be place in the state equivalent to the state where a force is exerted thereon from the external. If such a state can be created, it becomes easy to test as to whether or not the detector normarily operates.
(7) In the force detector having the above described sixth feature, the seventh feature resides in a force detector,
wherein the flexible substrate is constituted with a conductive material, and the first auxiliary electrode and the displacement electrode are formed by a portion of the conductive flexible substrate.
In the force detector having the seventh feature, the first auxiliary electrode and the displacement electrode are formed by a portion of the flexible substrate. Accordingly, the process step for newly forming the electrode is not particularly required. Thus, the structure becomes simple and the manufacturing cost can be reduced.
(8) The eighth feature resides in a force detector comprising:
a flexible substrate including a fixed portion fixed to a detector casing, a working portion to which a force is transmitted from the external, and a flexible portion having flexibility formed between the fixed portion and the working portion,
a fixed substrate fixed on the detector casing so as to face the flexible substrate,
a working body adapted to receive a force from the external to transmit this force to the working portion of the flexible substrate,
a displacement electrode formed on the surface facing to the fixed substrate of the flexible substrate,
a fixed electrode formed on the surface facing to the flexible substrate of the fixed substrate, and
a piezo electric element formed in a manner that it is put between the displacement electrode and the fixed electrode to transform an applied pressure to an electric signal by both the electrodes to output it to both the electrodes,
to detect a force exerted on the working body by an electric signal outputted from the piezo electric element.
In the force detector having the eighth feature, when a force from the external is applied to the working body, the flexible substrate is bent. Thus, a pressure is applied to the piezo electric element put between the displacement electrode and the fixed electrode. Since this pressure is outputted as an electric signal, an external force can be detected as an electric signal as it is.
(9) In the force detector having the above described eighth feature, the ninth feature resides in a force detector wherein a plurality of displacement electrodes are formed on one surface of the piezo electric element and a plurality of fixed electrodes are formed on the other surface, thus to detect a force exerted on the working body every plural directional components by electric signals obtained from the plurality of electrodes.
In the force detector having the ninth feature, it is possible to detect force components in plural directions by using a single piezo electric element.
(10) In the detectors having the above described first to ninth features, the tenth feature resides in a detector wherein the working body is constituted with a magnetic material to detect a force produced on the basis of a magnetic force exerted on the working body, thereby making it possible to carry out detection of magnetism.
2. Feature Relating to the Manufacturing Method
To attain the above-described second object, the manufacturing method according to this invention has the following features.
(1) In a method of manufacturing a physical quantity detector utilizing changes in an electrostatic capacitance, the first feature resides in a method comprising the steps of:
defining a working region, a flexible region adjacent to the working region, and a fixed region adjacent to the flexible region at a first substrate,
forming a first electrode layer on a first surface of the first substrate,
carrying out a processing for partially removing the first substrate in order to allow the flexible region to have flexibility,
connecting a first surface of a second substrate to a second surface of the first substrate,
cutting the second substrate to thereby form a working body connected to the working region of the first substrate and comprised of a portion of the second substrate, and a pedestal connected to the fixed region of the first substrate and comprised of a portion of the second substrate, and
forming a groove on a first surface of a third substrate to form a second electrode layer on the bottom surface of the groove to connect the third substrate to the first substrate so that the second electrode layer faces to the first electrode layer with a predetermined spacing therebetween.
In accordance with the manufacturing method having the first feature, a weight body or a magnetic body (these members are generically called a working body in this application) are formed by a portion of the second substrate, and a pedestal for supporting the first substrate is formed by another portion thereof. Namely, by cutting the second substrate, both the working body and the pedestal can be formed, so the physical quantity detector can be efficiently manufactured.
(2) In a method of manufacturing a physical quantity detector utilizing changes in an electrostatic capacitance, the second feature resides in a method comprising the steps of:
defining a working region, a flexible region adjacent to the working region, and a fixed region adjacent to the flexible region at a first substrate,
forming a first electrode layer on a first surface of the first substrate,
carrying out a processing for partially removing the first substrate in order to allow the flexible region to have flexibility,
connecting a first surface of a second substrate to a second surface of the first substrate,
cutting the second substrate to thereby form a working body connected to the working region of the first substrate and comprised of a portion of the second substrate, and a pedestal connected to the fixed region of the first substrate and comprised of a portion of the second substrate,
forming, on a first surface of a third substrate, a groove such that the working body can move with a predetermined degree of freedom, thereafter to connect the first surface of the third substrate to a second surface of the second substrate, and
forming a groove on a first surface of a fourth substrate to form a second electrode layer on the bottom surface of the groove to connect the fourth substrate to the first substrate so that the second electrode layer faces to the first electrode layer with a predetermined spacing therebetween.
In accordance with the manufacturing method having the second feature, a control member for limiting movement in a lower direction of the working body can be formed by a different substrates.
(3) In a method of manufacturing a physical quantity detector utilizing changes in an electrostatic capacitance, the third feature resides in a method comprising the steps of:
defining a working region, a flexible region adjacent to the working region, and a fixed region adjacent to the flexible region at a first substrate,
forming a first electrode layer on a first surface of the first substrate,
carrying out a processing for partially removing the first substrate in order to allow the flexible region to have flexibility,
forming, on a first surface of a second substrate, a groove such that the working region can move with a predetermined degree of freedom, thereafter to connect the first surface of the second substrate to a second surface of the first substrate,
forming a groove on a first surface of a third substrate to form a second electrode layer on the bottom surface of the groove to connect the third substrate to the first substrate so that the second electrode layer faces to the first electrode layer with a predetermined spacing therebetween.
As compared to the manufacturing method having the previously described second feature, the manufacturing method having the third feature becomes more simple.
(4) In the manufacturing methods having the above described first to third features, the fourth feature resides in a method in which a plurality of unit regions are defined on respective substrates to form single independent detectors every unit regions to finally separate them every respective unit regions.
In accordance with the manufacturing method having the fourth feature, it is possible to mass produce respective detectors.